sequential: Monotonically increasing ids with random increments.
The first 26 hex characters are random, the last 6 increment in
random amounts until an overflow occurs. On overflow, the random
prefix is regenerated and the process starts over.

Impact of UUID choices: the choice of UUID has a significant
impact on the layout of the B-tree, prior to compaction.

For example, using a sequential UUID algorithm while uploading a
large batch of documents will avoid the need to rewrite many
intermediate B-tree nodes. A random UUID algorithm may require
rewriting intermediate nodes on a regular basis, resulting in
significantly decreased throughput and wasted disk space space due to
the append-only B-tree design.

It is generally recommended to set your own UUIDs, or use the
sequential algorithm unless you have a specific need and take into
account the likely need for compaction to re-balance the B-tree and
reclaim wasted space.